A wide ratio range of transmission is generally advantageous for lowering loads of the engine and improving the fuel consumption rate of the vehicle due to allowing the vehicle to smoothly start and accelerate with the low load of the engine, as well as to cruise at high speed with the low revolution thereof. In case of the belt continuously variable transmission, the transmission ratio is defined by the ratio of the belt curvatures between the drive and driven pulleys. Therefore, the conventional continuously variable transmission has been made to have outer diameters and center distance of pulleys as large as possible, in order to obtain a wide ratio range. Meanwhile, both the belt transmitting efficiency and the ring damage have a characteristic to become extremely worse at vicinities of the ratio ends (i.e. low and overdrive ratio ends) of the pulley ratio range, and thus the wide pulley ratio range is rather considered not to be so preferable for the transmitting efficiency and endurance of the belt (i.e. the usable life of the belt). Nevertheless, in light of the whole automobile system, the wide pulley ratio range is considered to make a large contribution to alleviation of the engine load and improvement of the fuel consumption rate, even though it has such a demerit that may cause the degradation of the belt transmitting efficiency and the ring damage. It is thought that in the future the transmission is required for a lower revolution of the engine at vehicle cruise (i.e. an extended overdrive ratio end), a lower transmission ratio (i.e. an extended low ratio end) due to spread of turbo charged engines which is based on concept of downsized engine that can compensate low torque in low revolution range, and a higher transmission ratio (i.e. an extended overdrive ratio end) which can apply to high torque in middle and high revolution ranges. Therefore, the overall transmission ratio range (i.e. an overall ratio range) has an advantage for the above-mentioned requirements. Also, a continuously variable transmission is well known that an output portion of pulley unit has a planetary gear mechanism to be capable of having a wider overall transmission ratio than pulley ratio (See patent document 1: Publication No. JP3733893.). If outer diameters and shaft distance of the pulley unit are extended in order to have a wide pulley ratio range, a weight of pulley unit itself is supposed to increase due to extended outer diameter. In addition, a variable range of belt curvature radius at the pulley is extended and consequently, maximum value of the belt curvature radius becomes greater while minimum value thereof becomes smaller. When the belt curvature radius at the pulley is extended, the weight of pulley unit itself becomes much more increased due to satisfaction with requirement for rigidity. When the minimum value of the belt curvature radius at the pulley becomes smaller, a size of the belt becomes greater due to increments of operation frequency in high load range of the belt and consequently, a weight of belt itself becomes greater as well. In the meanwhile, when the shaft distance between the pulleys becomes greater, a total length of the belt becomes greater as well, thereby the weight of the belt itself becomes greater as well as the pulley. As described above, when outer diameters and shaft distance of the pulley unit are both extended, there occurs such a problem that a total weight of the transmission having the pulley unit increases due to weight increment of the pulley and belt. The conventional continuously variable transmission as disclose in the patent document 1 is thought to have similar problems concerning the above-mentioned weight increment as well. Also, When the outer diameters and the shaft distance of the pulley unit are both extended, a fuel consumption rate of the vehicle is deteriorated and an endurance of the belt is lowered since an operation frequency of the belt in range of high load becomes to increase and the pulley unit operates within a range where the belt has a low transmitting efficiency and a large ring damage.
Patent document 1: The publication of Japanese Patent No. JP3733893.